import fractions

def solve(N, M):
    gcd = fractions.gcd(N, M)
    N //= gcd
    M //= gcd
    m = M
    p2 = 0
    while m % 2 == 0:
        m //= 2
        p2 += 1
    p5 = 0
    while m % 5 == 0:
        m //= 5
        p5 += 1
    if m != 1:
        return -1
    if M == 1:
        Nstr = str(N)
        for n in Nstr[::-1]:
            if n != '0':
                return int(n)
    if p2 > p5:
        N *= 5 ** (p2 - p5)
    if p2 < p5:
        N *= 2 ** (p5 - p2)
    return N % 10

N = int(input())
M = int(input())
print(solve(N, M))